A. Field of the Invention
The present invention involves the field of cancer diagnosis and treatment. More specifically, the present invention relies on the identification and targeting of polymorphic forms of glutathione S-transferases (GSTs) in tumor cells.
B. Related Art
The glutathione S-transferases, or GSTs are a family of proteins whose best known function is the catalysis of the neutrophilic attack of the sulfur atom of glutathione by electrophilic groups of a variety of endogenous and exogenous compounds, including many mutagens, carcinogens, alkylating anticancer agents and electrophilic products of xenobiotic metabolism (Mannervik and Danielson, 1988; Pickett and Lu, 1989; Hayes and Pulford, 1995; Commandeur et al., 1995). The currently known human soluble GSTs are classified into four groups, .alpha., .mu., .pi. and .theta. according to their N-terminal amino acid sequence homology, enzymatic substrate specificity, and antigenicity (Mannervik et al., 1992).
GSTs are involved in many cellular functions, the best characterized of which is their role as phase II enzymes in which they catalyze the S-conjugation of glutathione (GSH) with a wide variety of electrophilic compounds, including many mutagens, carcinogens, anticancer agents and their metabolites (Mannervik, 1985; Mannervik and Danielson, 1988; Pickett and Lu, 1989; Daniel, 1993; Boyland and Chasseaud, 1969; Coles and Ketterer, 1980; Ketterer and Sies, 1987; Sato, 1989; Morrow and Cowan, 1990; Waxman, 1990; Tsuchida and Sato, 1992; Commandeur et al., 1995).
Significant over-expression of the GST-.pi. gene is associated with malignant transformation, tumor drug resistance, and poor patient survival (Sato, 1989; Morrow and Cowan, 1990; Waxman, 1990; Tsuchida and Sato, 1992; Commandeur et al., 1995; Tidefelt et al., 1992; Muramatsu et al., 1993; Gilbert et al., 1993; Tew, 1994), and in many human tumors and pre-neoplastic lesions, the GST-.pi. protein is over-expressed, even though, in the corresponding normal tissues the protein is either absent or expressed at very low levels.
The GST-.pi. gene has been mapped to a relatively small region of chromosome 11q13 which contains a number of cancer-associated genes and proto-oncogenes, including, bcl1/prad1, int2 and hstf1, some of which have been reported to be co-amplified with the GST-.pi. gene in some tumors (Lammie and Peters, 1991; Saint-Ruf et al., 1991). In human malignant gliomas, a positive correlation has been demonstrated between the level of GST-.pi. expression (by immunocytochemistry) as well as both the histological grade of the tumor and patient survival (Saint-Ruf et al., 1991; Hara et al., 1990). An association between high GST-.pi. protein expression and 2-chloroethylnitrosourea resistance in some human glioma cell lines also has been demonstrated (Ali-Osman et al., 1990).
The nucleotide sequences of the complete human GST-.pi. cDNA and GST-.pi. gene reported to date from a variety of sources (Kano et al., 1987; Moscow et al., 1988; Cowell et al., 1988; Morrow et al., 1989) suggest that only one human GST-.pi. gene exists (Mannervik et al., 1992). The isolation of two different GST-.pi. proteins (Ahmad et al., 1990) from human placenta, however, strongly suggests that genetic polymorphism may exist in the human GST-.pi. gene locus. Whether or not this putative polymorphic nature plays a role in tumorigenesis remains unclear, and thus it is important to explore both the structural and functional variation in this gene locus.